The invention relates to a feed device for a high-pressure roller press for the high-pressure comminution of grinding stock, said feed device delivering the grinding stock in a controlled manner into the roller nip between two rollers of the high-pressure roller press.
For the comminution of brittle grinding stock, Schönert in 1977 proposed in German Auslegeschrift DE 27 08 053 not to comminute the grinding stock in traditional fashion, but firstly, through the application of high pressure in a roller nip, to press the grinding stock into flakes, whereupon the structure of the grinding stock ruptures. In a further step, the flakes emerging from the roller nip can be broken down into their individual component parts using comparatively little energy. The high-pressure pressing in the roller nip and the subsequent disagglomeration of the pressed flakes demands less energy for the comminution per unit of mass of grinding stock than does a conventional grinding process. Through this type of comminution, high grinding finenesses are attainable, for which purpose a circulation of the grinding stock is necessary. Since the roller nip, however, is wider than the greatest extent of the comminuted grinding stock, it is important to charge the roller nip such that, at the same time, a specific quantity of the grinding stock passes through the roller nip. If the roller nip is charged with too small a quantity per unit of time, then in the extreme case the grinding stock is no longer comminuted at all or the high-pressure roller press acts similarly to a crusher. If, on the other hand, too large a quantity is poured onto the roller nip, it can happen that the high-pressure roller press is overloaded and starts to vibrate. Upon the vibration, the roller nip gets larger and smaller in terms of resonance frequency and also the circulation speed varies with resonance frequency, since, in the event of an overload, the rollers of the high-pressure roller press are repeatedly braked by the excess of grinding stock and re-accelerated by the drive motors. In the case of high-pressure comminution in the roller nip, care must therefore be taken to ensure that the roller nip is supplied with grinding stock in suitable measure. The actual feed quantity is heavily dependent, however, on the nature of the grinding stock. The noteworthy parameters to which regard should be paid are the grain size distribution, the mean grain size and the evenness of the available stream of grinding stock onto the roller nip. For the delivery onto the roller nip, the grinding stock or ‘feed material’ must be fed evenly into the roller nip from above.
The type of material charging has a significant influence on the smooth running of the high-pressure roller press. In order to improve the feed conditions and ensure an even distribution of the drive power to the drive motors of the high-pressure roller press, the working of a feed device above the roller nip is therefore being steadily improved.
German Offenlegungsschrift DE 34 38 310 A1 discloses a device for evening out the delivery of feed material via a feed gate into a comminuting machine, wherein the feed material is repeatedly redirected.
In German Offenlegungsschrift DE 40 06 971 A1, a feed device for filling granular solids into a comminuting machine is disclosed, wherein a pipe resonator is disposed between a hopper and the comminuting machine.
Finally, German Offenlegungsschrift DE 196 32 976 A1 and corresponding U.S. Pat. No. 5,876,648 discloses a feed device which divides the feed material into two fractions by means of a screen and delivers the fractions from different sides onto the roller nip of a high-pressure roller press.